One of the essential concerns of internal combustion engine makers and of motor oil manufacturers is to develop new mechanical methods and new lubricating compositions making it possible to reduce wear and/or fuel consumptions.
It has, in particular, been sought to lessen the viscosity of the lubricating oil base, but the risk is then premature wear of the engines. To reduce that wear, it has been proposed that products be used to adjust the viscosity of oils, such as polymethacrylates, polyisobutylenes and the so-called antiwear additives with a sulfur, phosphorus and a heavy metal base like metal dithiophosphates.
The viscosity regulators have the disadvantage of being sheared on use, which reduces their effect, and of breaking down thermally, forming varnishes harmful to engine endurance. Furthermore, the sulfur, phosphorus and heavy metal base antiwear additives have a limited lifetime.
It has also been proposed that microdispersions of solid lubricants, such as molybdenum disulfide (MoS.sub.2) and graphite, be added to oils as antiwear additives, but the results are poor as far as the fuel economy obtained is concerned.
An appreciable improvement has been made by reinforcing the action of sulfur, phosphorus and heavy metal base additives with polar derivatives, such as esters of fatty acids and alcohols, e.g., isopropyl oleate.